Date of Award

December 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Robert Cuzner

Committee Members

Hossein Hosseini, David Yu, Ilya Avdeev, Chiu Law

Abstract

Power electronic converters rated for medium voltage direct current (MVDC) are promising for electrification of future ships. In shipboard electrification, due to limitation of space, energy and technical maintenance, the high-power density, high efficiency and modularity of the power electronic converters are desired. Utilizing power modules made from wide band gap (WBG) semiconductors like silicon carbide (SiC) and high frequency power transformer (HFPT) can be beneficial for obtaining the high-power density, high efficiency and isolation that is required for the power electronic converters. To provide power for the low voltage (LV) DC loads, a conversion of the power from MVDC main bus to LVDC is needed. Therefore, a DC-DC converter is an essential component of a DC power system. DC-DC converter is a multipurpose element in Unit-based protection architecture (UBPA) which is an architecture that eliminates the need for DC circuit breaker (CB) and instead relies on isolated power electronic converters for protection of the system. Topologies based on Dual active bridge (DAB), Neutral point clamp (NPC) and Modular Multi-level Converter (MMC) are suggested for such a DC-DC converter rated for megawatt (MW) power level. Switching at MV level with high frequency in the ship environment is challenging because of the parasitic coupling that appears between the power module, MV side of the transformer and the ship haul which is made from the materials capable of conducting electricity. Moreover, the transformer used in the isolated DC-DC converter is one of the main contributors to the weight and power density of the converter. In this study, the DAB converter is suggested as a building block for an input series output parallel (ISOP) connected converter and analytical equations are provided for the design. A novel design for the HFPT is proposed and analytical formula is derived for the thermal loss and the leakage inductance of the HFPT. Optimization methodology using evolutionary algorithms method like genetic algorithm is applied to the design to extract the optimal values for a design. A case study is also provided in this study.

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